Atty. Gen. Eric H. Holder Jr., recused from the Justice Department investigation into who tipped off the Associated Press about a CIA operation, says the 'very serious' leak endangered American lives.

WASHINGTON — Atty. Gen. Eric H. Holder Jr. on Tuesday strongly defended the criminal investigation into the leak of classified details about a successful U.S. undercover operation, calling it "within the top two or three most serious leaks" of government-protected information since he became a federal prosecutor more than 35 years ago.

The attorney general said he had recused himself earlier from overseeing the investigation into who told the Associated Press about the disruption of a bombing plot in Yemen because the FBI had interviewed him about the matter a year ago. He said Deputy Atty. Gen. James Cole was overseeing the inquiry, which is being run by Ronald C. Machen Jr., U.S. attorney in Washington.

But Holder did not hesitate to defend a decision he said he did not make: to subpoena two months' worth of telephone records from more than 20 Associated Press telephone lines. He said American lives had been endangered by the disclosure.

It was "a very, very serious leak," Holder said. "It put American lives at risk, and that is not hyperbole. It put the American people at risk."

Prosecutors want to know who tipped off the Associated Press about the secret CIA operation that foiled a plot to bomb an airplane bound for the U.S., an attack that was to coincide with the one-year anniversary of the killing of Al Qaeda leader Osama bin Laden.

The story, published May 7, 2012, said Al Qaeda operatives had devised a new type of bomb without metal, making it easier to evade airport security. The Associated Press reported that the terrorists had not yet selected a target city or purchased a plane ticket "when the CIA stepped in and seized the bomb."

Holder is one of two top government officials, along with CIA Director John Brennan, who has revealed that he was interviewed in the leak investigation, a sign that authorities have examined whether details about the foiled plot came directly from a senior Obama administration source.

The Reporters Committee for Freedom of the Press and dozens of media companies — including the Tribune Co., owner of the Los Angeles Times — objected to prosecutors' conduct. "None of us can remember an instance where such an overreaching dragnet for news-gathering materials was deployed" since the government issued guidelines for such cases 30 years ago, the journalists said in a letter to Holder and Cole. They called on prosecutors to return the records or at least to segregate and prevent further use of them.

Cole wrote to Gary B. Pruitt, president and chief executive of the Associated Press, defending the decision to subpoena the office and personal phone records.

Cole echoed Holder's characterization about the enormity of the leak, saying it posed "grave harm to the security of all Americans." He deflected complaints that the subpoenas were overly broad or chilling to 1st Amendment rights.

The subpoenas were "limited to a reasonable period of time and did not seek the content of any calls," he said, and the records "cover only a portion" of two months last year.

"These records have been closely held and reviewed solely for the purpose of this ongoing criminal investigation," Cole said. "The records have not been and will not be provided for use in any other investigations."

He added: "We strive in every case to strike the proper balance between the public's interest in the free flow of information and the public's interest in the protection of national security and effective enforcement of our criminal laws. We believe we have done so in this matter."

Holder said that although he was not privy to the investigation, he was sure it was being conducted "in conformance with [agency] regulations." He added: "I'm confident the people who are involved in this investigation followed all of the Justice Department regulations and did things according to [agency] rules."

The Associated Press said it had held off publishing details about the plot for a week because of the sensitivity of the matter. The wire service said it went ahead after it was told that "those concerns were allayed."

But U.S. officials said the disclosures put a secret informant and his family at risk and cut off his opportunity to continue to gather intelligence.

At the White House, spokesman Jay Carney said President Obama had learned of the seizure of phone records Monday during a fundraising trip to New York. Carney offered little insight into how the president, a former constitutional law professor, responded.

Carney, a former reporter, said Obama supported journalists' right to pursue investigative stories "unfettered," but believed that right should be balanced with the need to protect national security.

"The president has confidence in the attorney general," Carney said. "He has confidence in his team over at the Department of Justice."